Belphegor is a demon of Sloth, one of the 7 Deadly Sins. His name is a corruption of Baal-Peor, the name for the god of the Moabites. Belphegor gives people ideas for inventions that will make them rich and thus greedy and selfish. Sometimes is portrayed as a beautiful woman, but other times is portrayed as a monstrous, horned demon.
Some claim that he must be worshipped on a toilet, thus we get his design in the Shin Megami Tensei games.
Belphegor is an extra boss found in Belphegor's Tower, a dungeon which can only be reached if the hero has its key, which he receives after returning the lost kid found in Moloch's Temple. After his defeat, the hero obtains the Vajra, the best weapon for the Partner. He is later fought in the final dungeon, Suzuki Company Ltd., right before Satan.
Before the story began Phegor was kidnapped and sealed away by the demons of Fire and Light from Muspelheim. The Fake one would later seal away the real Zebul. When Akira defeats the Fake Berith he would express shock and stand in his way to prevent him from meeting the Fake Zebul. After his defeat he would transform into his true demonic form and disappear. Like the other Fake Brothers the difference between the real one and fake one is the skin tone and face.